Terror fears as deadly cargo heads for UK waters

Two British ships carrying the world's first seaborne cargo of weapons-grade plutonium - enough to make 40 nuclear bombs - will sail into UK waters under armed guard this week, amid heightened concern over a maritime terrorist attack.

Holding 140kg of plutonium from US atomic missile warheads, the Pacific Pintail and Pacific Teal will place millions at risk if disaster strikes. Ex-government nuclear physicists, experts on international terrorism as well as former Ministry of Defence staff have described the trip as absurd in the wake of fresh intelligence that al-Qaeda is plotting to target Western shipping interests.

Nuclear security officials will monitor the ships' progress from a secret London-based headquarters as the merchant vessels enter the world's busiest waterway, the English Channel. Their arrival follows a statement by the head of the Royal Navy, Admiral Sir Alan West, that he had specific intelligence that al-Qaeda was seeking to blow up merchant ships, particularly those navigating congested shipping routes.

Although the government has remained tight-lipped over details of the voyage, an Observer investigation can reveal the true extent of Britain's involvement in the controversial shipment. Documents show that the ships' security was assessed and approved principally by British nuclear security officials. It has also emerged that 13 armed British commandos will stand guard on the decks of each vessel. The boats are the property of government-owned company BNFL. Once ordinary commercial ships, both are now equipped with 30mm cannon.

The cargo is destined for a nuclear reprocessing plant in France, where it will be converted for use as commercial fuel. If successful, the US wants to transfer thousands more kilogrammes of plutonium to Europe. At the end of the Cold War, the US and Russia promised to dispose of nearly 70,000kg of the material from dismantled nuclear warheads. But opponents claim the nuclear industries of both countries, along with Britain and France, should have resisted the opportunity to turn plutonium into commercial fuel and disposed of it safely as waste.

The Pintail and Teal will enter UK waters on Thursday and are expected to sail within 16 miles of Cornwall's Lizard peninsula on Saturday before passing close below the Devon, Dorset and Hampshire coast and docking in Normandy. Environmentalists believe the narrow and often stormy Channel remains the most likely leg of the 2,000-mile voyage for potential disaster. More than 400 vessels pass through the waterway each day.

Critics warn that the Pintail and Teal represent a valuable target for rogue states and terrorists seeking to acquire nuclear capability. Scenarios discussed by both UK and US intelligence are believed to include those where a vessel is not only seized but attacked by missile or rammed by boat or aircraft. The ships are relatively slow, with a top speed in the region of 15 knots, leaving them unable to outpace more modern vessels.

Dr Frank Barnaby, former nuclear physicist with the UK Atomic Weapons Establishment, said: 'The consequences of an attack could be enormous. I cannot understand why they don't use a proper warship, given that in the event of an attack or collision where there is a fire in the cargo then the contamination potential is catastrophic.'

Others warn that it is the weather that represents the gravest threat. Sir Timothy Garden, former assistant chief of defence staff at the MoD and ex-director of the Royal Institute of International Affairs, said: 'There are lots of reasons why shipping plutonium is not a good idea, but vessels going down to bad weather seems a greater risk than terrorism.'

The boats are expected to dock at Cherbourg a week today, where a flotilla of protesters will jeer their arrival. From there, the warheads will be transported 800 miles by road to a reprocessing plant in Provence.